Panic disorder is a severe anxiety disorders characterized by significant disability. Rats in which GABA inhibition is chronically disrupted in the dorsomedial hypothalamus/perifornical (DMH/PeF) region, exhibit heightened anxiety and panic-like responses, defined as increases in heart rate (HR), mean arterial pressure (BP), respiratory rate (RR), and anxiety as measured by the social interaction (SI) test, following exposure to subthreshold cues such as 0.5 M sodium lactate and 7.5% CO2, agents known to provoke panic attacks in subjects suffering from panic disorder. During the last funding period, we have extensively characterized the afferent pathways for the lactate stimulus, demonstrated some of the regulatory mechanisms within the DMH, and identified the efferent targets of the DMH that are implicated in the panic-like response. The goal of this competitive renewal (MH 52619) is to further elucidate the pathways and neurotransmitters involved in the different components of panic response using pharmacological, functional neuroanatomical, and molecular studies. Overall Hypothesis of the work is that disruption of GABA inhibition in the DMH/PeF region of rats induces a 'panic-prone'state, as a result of pathological activation of a select group of glutamate/peptidergic projection neurons, most prominently orexin/dynorphin A (ORX/DYN) positive cells. This results in aberrant stimulation of a number of efferent targets from the DMH. During this funding period, we will study the pathways involved in activating the bed nucleus of the stria terminalis (BNST) to result in anxiety-like responses and specific brain stem projection targets such as the nucleus tractus solitarius (NTS) in causing inhibition of parasympathetic and activation of sympathetic pathways to increase HR and BP following lactate infusions in these panic-prone rats. We will test these hypotheses with experiments using neuronal immunohistochemical studies;systemic injections of ORX and other peptide receptor antagonists;targeted lesioning of the ORX neurons in the DMH/PeF;measuring the changes in pre-proORX (ppORX), proDynorphin (pDYN) and other peptide mRNA expressions using RTPCR;and acute ppORX and/or pDYN gene knockdown with siRNA, within the DMH. We will study the efferent sites with infusions of pharmacological agents, gene silencing using siRNA as well as neuroanatomical techniques. Finally, we will study the role of local versus extrinsic GABA neurons by GAD-67/65 gene silencing in the DMH/PeF region.